Electromagnetic detectors or sensors such as those commonly used in light detector systems are commonly known in the art. One type of light detector system uses infrared detectors to detect the presence of infrared light. One diode sends out an infrared light signal. A second infrared LED detector produces a small electric signal when it receives an infrared light signal. When an object comes within range of the emitted signal, it reflects the light back onto the detector LED. This causes the detector LED to produce an electric signal that is sent into the detection system. In other light detection systems, a light emitter transmits a beam of light across a detection region where the light is detected by a light detector. If an object, e.g., a person, interrupts the light beam, the light detector senses the interruption, thus indicating the presence of an object or person within the detection region (referred to as a “beam break”). Infrared light detector systems are thus often used in motion detection, people detection or “people counting” systems that may be part of larger security systems.
Light detectors or sensors such as those used in infrared light detector systems typically have an incident viewing angle of close to 180 degrees, making the light barrier (and beam break) of the sensor susceptible to interference caused by extraneous light sources, which may contain the infrared wavelength, such as sunlight, neon signs, and automatic door openers. Often, a light barrier system incorporates a shroud used to block light exceeding the desired angle of incidence, having an aperture with an aspect ratio of depth greater than the width, e.g., a cylinder, so that the sensor only receives light from the intended emitter that is directly across from the sensor. However, due to the size of the hardware used on the sensor and the extremely limited space the sensor may occupy, the maximum height of the light shroud cannot exceed certain dimensions, such as, for example, 0.763 mm (0.03 inches). Many of the sensors currently using shrouds to block some of the unwanted light from extraneous light sources exceed this maximum thickness, rendering the sensor virtually useless in many light detection systems.
Therefore, what is needed is a mechanism that blocks the unwanted light impinging upon the sensor of the light detector system, yet allows enough intended light through for the sensor to work efficiently while complying with thickness and design constraints.